1. Field of the Invention
This invention relates to a closed loop system wherein abrasive is blasted against a surface to be cleaned and is then recovered for reuse in the system, through the use of means for removing trash, debris, dust therefrom.
2. Brief Description of the Prior Art
Surface blasting recovery systems of the prior art have failed to provide adequate separation of trash, debris and dust from the abrasive employed therein. Since the abrasive is ultimately sent back to a blasting apparatus for reuse, it is imperative that it be free of such foreign matter. Many problems may result from the failure to adequately perform such separation. Clogging of system components and increased wear and tear on the blasting mechanisms are but a few of such problems. Moreover, the health of the user may be endangered if dust is permitted to remain with the recycled abrasive during blasting, or if dust is not separated from the debris prior to disposal.
In failing to recognize the importance of metering the input material to be recovered as an aid in classification, many prior art systems have attempted to separate debris from abrasive in great amounts. The intake portions of such systems are usually large and the walls thereof are configured such that abrasives and foreign matter generated by the blasting process, impinge thereon. Although such inlets may function to decrease the kinetic energy of the recovered materials, the volume of materials entering the system makes difficult the later classification thereof. This problem is common to the systems described in U.S. Pat. Nos. 4,693,041, 4,753,052, 4,788,799 and 5,090,162.
In one of these systems, that described in U.S. Pat. No. 4,693,041, abrasive is separated from dust via magnetic members and a single filter screen. Air flow is such that dust and debris are carried past the magnetic members. However, the likelihood of debris remaining with abrasive is high when recovered in large amounts, since debris will impinge on the magnetic members due to the large volume of air laden debris traveling therethrough. Thus, a large portion of the debris traveling through the system may lose kinetic energy after impinging on the magnetic members, only to fall through a filter screen and remain with the abrasive.
Additionally, In U.S. Pat. No. 5,090,162 a blasting apparatus is disclosed wherein the mixture of abrasive material, dust and debris are collected through a rebound corridor. Dust and debris are separated by passing the mixture through funnels wherein lighter particles are separated from heavier ones due to air flow. Should heavy debris be collected, however, it is unlikely that this system would work effectively, as such debris would have a tendency to remain with the heavy abrasive, thereby contaminating it.
Despite the absence of means for metering incoming particles, many systems do not have classifiers which can adequately separate large or heavy matter from the blasting abrasive. An example of such is the system of Published European Patent Application No. 0274783. This system is of limited application, as such could not be used to clean a structure wherein large particles would be created. Separation of large particles from the abrasive could not occur in this system because large particles would remain on the sieve and eventually clog the system.
Similarly, in GB-1539571 a separator is disclosed wherein a high pressure blower is employed to separate abrasive material from dust and debris. The potential for a great deal of debris and dust remaining with the recovered abrasive exists due to the absence of a material classifier. This separation system will not be able to distinguish between heavy debris and abrasive shot, as this system is dependent solely on the abrasive shot being heavier than debris for effective separation to occur.
In those systems where classification does occur, many of the classifiers are inadequate. In U.S. Pat. No. 4,773,189 a separation system is disclosed wherein polymeric material is separated from debris and dust through a series of screens. However, any heavy debris which is not separated by the screens will be contained with the polymeric material in the storage hopper, and potentially fed back to the blaster.
The failure to adequately separate debris from dust after abrasive has been separated therefrom, has been a problem inadequately dealt with in the prior art. In many systems, both dust and debris are disposed of together, such as in the systems above and in the systems disclosed in U.S. Pat. Nos. 4,993,200, and 5,134,810. In U.S. Pat. No. 4,993,200 a blasting apparatus is disclosed wherein dust and debris are separated from abrasive by a classifier. However, in these systems the dust and debris are not separated from one another. Thus, upon the disposal thereof, dust comprising undesirable contaminants is permitted to escape into the air and causes damage to the environment. In U.S. Pat. No. 5,134,810 disclosed is an abrasive cleaning machine wherein abrasive particles are recovered from a mixture solely through the use of vacuums. However, no classification of debris or separation of dust therefrom, takes place, as both are disposed of together.
Some prior art systems have developed means for containing dust separately. However, dust is usually only separated and accumulated once throughout the system and is never a further concern. Thus, upon the final separation of debris from the abrasive, often there is a great deal of accompanying dust which is neither recovered nor contained. An example of systems in which such a problem exists is U.S. Pat. No. 5,035,089 and Published European Patent Application No. 0274783.
In U.S. Pat. No. 5,035,089 a blast media recovery system is disclosed wherein dust is initially separated from debris and abrasive. However, problems associated with dust remaining with the mixture of debris and abrasive, is not alleviated by the later separation of debris from abrasive, carried out by a multiscreen separator. Thus, such uncontained dust leads to problems of contamination of the abrasive which may result in ineffective cleaning, as well as damage to the environment and endangerment of the health of the user. A similar abrasive blasting apparatus is disclosed in Published European Patent Application No. 0274783. The recovered abrasive is separated from dust via baffle plates and a screening sieve. Dust is initially separated from the abrasive and sent to a dust collector. Whatever dust is not recovered is then allowed to remain with the abrasive for reuse.
The present invention overcomes all of the above inadequacies of the prior art and provides a system wherein particles comprising abrasive, trash, debris and dust are received from the blasting area, and applied to a novel multistage screening and airwash system. The abrasive is ultimately recycled for reuse is free trash, debris and dust, each of which are disposed of separately.